Computational and Experimental Studies on the Adsorption of CO, N2, and CO2 on Mg-MOF-74

Adsorption of carbon monoxide, dinitrogen, and carbon dioxide on the porous metal organic framework Mg-MOF-74 was investigated by means of a combined methodology comprising variable-temperature infrared spectroscopy and ab initio periodic DFT-D calculations using the CRYSTAL code. Both CO and N-2 were found to form nearly linear (Mg2+center dot center dot center dot CO and Mg2+center dot center dot center dot NN) adsorption complexes, in contrast with CO2, which forms an angular Mg2+center dot center dot center dot OCO complex. From IR spectra recorded at a variable-temperature, the standard adsorption enthalpy (Delta H-0) was found to be -29, -21, and -47 kJ mol(-1) for CO, N-2, and CO2, respectively. Calculated values of Delta H-0, including an empirical correction for dispersion forces, resulted to be in a reasonably good agreement with those experimentally obtained. Calculations also showed the very significant role played by dispersion forces, which account for about one-half of the adsorption enthalpy for each of the three adsorbates, CO, N-2, and CO2. The results are discussed in the broader context of the adsorption of the same gases on other MOFs and also on zeolites.